Contact lenses are commonly provided to the consumer in containers in the form of plastic packages. A typical package includes defines one or more cups each suitable for holding a contact lens. Each cup is usually filled with saline solution that immerses the contact lens, and maintains the contact lens in a hydrated condition. The cup may be covered by a piece of aluminum foil, or other suitable material, applied to the package after the contact lens and saline solution are introduced into the cup. The packaging process is typically performed using automated equipment centrally controlled by a programmable logic controller or other suitable control device.
The cups of the packages may be filled using pumps that deliver a metered dose of saline solution. The centralized control device can be programmed to check whether each pump delivers a dose of saline solution to an associated cup. The controller can perform this function by monitoring whether the pump activates while the cup is positioned to receive saline solution from the pump. A secondary check can be performed before the cup is covered and sealed to verify that saline solution has been delivered to the cup.
The secondary check can be performed using a photoelectric proximity sensor that emits infrared light toward the cup. Saline solution, if present in the cup above a certain level, will reflect the infrared light. The proximity sensor, in turn, can detect the reflected light of a predetermined intensity, as measured by the proximity sensor, can be interpreted as an indication that saline solution is present in the cup above a certain level, e.g., above the half-full mark.
The operation of the sensor is dependent upon alignment of the sensor and the cup. In particular, the infrared beam emitted by the sensor may need to be focused precisely at the apex of the meniscus of the saline solution for the proximity sensor to provide an accurate indication of whether saline solution is present in the cup. The degree of alignment required for the proximity sensor to function optimally may be difficult to achieve and maintain in a production environment.
The operation of the proximity sensor can also be dependent upon the orientation of the meniscus of the saline solution. For example, air bubbles often form in the meniscus during filling of the cup and can alter the orientation of the meniscus, so that the beam of the proximity sensor is no longer focused at the apex of the meniscus. The sensor may issue false readings under such circumstances. In particular, the sensor may falsely indicate that the package does not contain saline solution, leading to an unwarranted rejection of the package and the associated contact lens.